从全英文词典dictionary.com来看,
urban(adj)means of,relating to,or located in a city /
Characteristic of the city or city life.
downtown(adj)means of,pertaining to,or situated in the main business section of a city
所以我认为哦,urban 主要指城市的,市内的,
而downtown 主要指市中心的,商业区的（最繁华的街区,就像南京新街口）